Authorities have declared a number four alarm fire -- the second highest level -- for the blaze at Wang Fuk Court in Tai Po, a district in the northern part of the Chinese finance hub.

At least one man and one woman were rushed to hospital while unconscious and with severe burns, police told local media.

A firefighter was also reportedly injured, while police earlier received reports of residents trapped in the buildings, according to media.

Thick plumes of smoke were seen billowing from the construction scaffolding on multiple towers, footage on local media showed.

Authorities closed sections of a nearby highway as the firefighting operation continued on Wednesday afternoon.

"Residents nearby are advised to stay indoors, close their doors and windows, and stay calm. Members of the public are also advised to avoid going to the area affected by the fire," the Fire Services Department said.